How to Identify Storage Requirements for Your ZFS
Storage Pool

Determine available devices.

Before creating a storage
pool, you must determine which devices will store your data. These devices
must be disks of at least 128 Mbytes in size, and they must not be in use
by other parts of the operating system. The devices can be individual slices
on a preformatted disk, or they can be entire disks that ZFS formats as a
single large slice.

ZFS supports multiple types
of data replication, which determines what types of hardware failures the
pool can withstand. ZFS supports non-redundant (striped) configurations, as
well as mirroring and RAID-Z (a variation on RAID-5).